1. Field of the Invention
The present invention relates to an electrical variable optical attenuator for use in optical fiber communications and for use with optical network technology, and particularly to an electrical variable attenuator with a mechanism for holding the orientation of an attenuation filter without inducing trembling of the filter.
2. Description of Related Art
An optical attenuator is a passive optical component for reducing optical power propagating in an optical fiber, and may perform fixed or variable attenuation. Optical attenuators are widely used in optical mission systems and optical networks.
A general variable attenuator has a filter. The filter has an effective filter region disposed in the optical path between a collimator and a reflector. The filter has a filter density which varies from a low density region to a high density region. The transmitted light is attenuated to different intensities by linear movement of the filter across the optical path of the light.
For example, U.S. Pat. No. 6,130,984 discloses an electrical variable optical attenuator comprising a filter mounted on a wiper for being selectively positioned within the optical path of a light beam, a screw for guiding and coupling with the wiper, and a motor for driving the screw to rotate. The wiper and the screw keep relatively stable along the intended axial center line of the screw. Changing the axial center line of the screw, however, causes the axial center line of the wiper and the filter to change with respect to the optical path of the light. When the motor drives the screw to rotate, the screw and the filter tremble slightly. This trembling affects the attenuated value and its precision.
The present invention provides an electrical variable optical attenuator which has a mechanism for precisely orientating the filter and avoiding trembling of the filter.
An object of the present invention is to provide an electrical variable optical attenuator, and particularly to provide an electrical variable attenuator having a mechanism for orientating the filter while avoiding trembling of the filter.
An electrical variable optical attenuator of the present invention comprises a cover, a housing, an optical module, an attenuating means, an electrical driving element, an input fiber and an output fiber.
The electrical driving element comprises a screw, a stepping motor, a pin holder and a resistor. The stepping motor drives a screw rod. The stepping motor controls the direction and speed of the screw rod according to the resistance provided by the resistor. The screw rod drives the attenuating means.
The attenuating means comprises a carrier, a filter and a sliding patch. The carrier has an insertion slot on top of the carrier for fixing the filter therein, a guide groove in a bottom of the carrier, and an inner screw and a slot separately defined in both sides of the carrier. The sliding patch is fixed in the slot and comprises a wiper portion for contacting with the resistor. The filter has a varying optical density gradient along at least one of its dimensions.
The optical module has a guide pole, a first mirror, a second mirror, a through hole, a pair of containing grooves, and a guide hole. The containing grooves separately fix fiber collimators attached to ends of the input and output fibers, holding them parallel to one another and directed towards the two mirrors. The through hole is defined in a sidewall of the optical module. The guide pole is received in the guide groove of the carrier for confining the movement of the carrier along the screw rod, thereby avoiding trembling of the screw rod during rotation of the screw rod.
In assembly, the resistor of the electrical driving element is received in a cavity of the optical module. The guide pole of the optical module is received in the guide groove of the carrier. The screw rod of the electrical driving element extends through the through hole and engages with the inner screw of the attenuating means. The wiper portion of the attenuating means contacts with the resistor of the electrical driving element. The optical module and the electrical driving element are fixed together and fixed into the housing.
Other objects, advantages, and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.